(Linnaeus, 1758)
Loggerhead turtle
Recognition
This is a large (to 123 cm, but more typically 85-100 cm) sea turtle with five or more pairs of pleurals (the 1st touches the cervical), and three poreless inframarginals on the bridge. The elongated carapace has a medial vertebral keel that becomes progressively smoother with age, is highest anterior to the bridge, and is serrated posteriorly. No lateral fontanelles occur in adults. All vertebrals are broader than long; neural bones 7-11 are hexagonal, shortest anteriorly, and may be separated. The marginal scutes average 12 or 13 on each side but vary from 11 to 15. There are 12-13 pairs of peripherals; the 9th and 10th pairs are separated from the ribs. The posterior marginal rim is serrated in juveniles, but becomes smoother with age. The carapace is reddish brown but may be tinged with olive; the scutes are often bordered with yellow. Bridge and plastron are yellow to cream colored. The plastron is hingeless and has two longitudinal ridges, which disappear with age. The plastral formula is: an > abd >< fem > hum > pect > gul > intergul; the intergular scute is very small, and may be absent. The large head is broad posteriorly and rounded in front; its snout is short and broad, and there are two pairs of prefrontals and three postoculars. The head varies from reddish or yellow chestnut to olive brown, often with yellow-bordered scales. No ridge occurs on the triturating surface of the yellowish brown jaws, and the bony surface of the lower jaw is smooth at the symphysis. The vomer neither separates the maxillae nor touches the premaxillae. The descending prefrontal processes touch both the vomer and palatines. The frontal does not enter the orbit, and there is a blunt ridge on the vomer and palatines. Limbs and tail are dark medially and yellow laterally and below. Two claws occur on the forelimbs. Adults usually weigh about 100-150 kg, but truly massive size is sometimes attained. Caretta probably is the largest living hard-shelled turtle; it is exceeded in length and weight only by the leatherback (Dermochelys coriacea). Weights up to 450 kg have been recorded and there is a skull in the Bell collection at Cambridge University of such width (28.4 cm) as to indicate a weight of about 540 kg (Pritchard, 1967).
As in other species of Cheloniidae, the loggerhead has 56 diploid chromosomes: 32 macrochromosomes (12 metacentric, 2 submetacentric, 6 subtelocentric, 12 acrocentric) and 24 microchromosomes (Kamezaki, 1989).
Males have narrow shells gradually tapering posteriorly, and long, thick tails, extending beyond the rear carapacial margin.
Distribution
Caretta occurs in the Pacific, Indian, and Atlantic oceans from Washington, Japan, India, Kenya, the British Isles, and Newfoundland south to Chile, Australia, South Africa, tropical western Africa, and Argentina. It also occurs in the Caribbean and Mediterranean seas. Carr et al. (1980) have discovered loggerheads hibernating in the Port Canaveral ship channel off the east coast of Florida.
Caretta caretta is the only marine turtle with a nesting range that lies mostly beyond the tropics. Nestings have been recorded in the United States from New Jersey south to Florida and west to Texas, but most of the North American breeding range lies in South Carolina, Georgia, and Florida (Dodd, 1988; Ernst et al., 1994). Other breeding beaches that possibly contribute individuals to Atlantic waters are located in Brazil, French Guyana, Surinam, Guyana, Venezuela, Colombia, Costa Rica, Nicaragua, Honduras, Guatemala, Belize, Mexico, Trinidad, Tobago, Grenada, St. Lucia, Dominica, Antigua, Hispaniola, Cuba, Cayman Islands, Dry Tortugas, and the Bahamas (Dodd, 1988; Pritchard, 1988). It also nests in Sicily, Sardinia, Italy, Greece, Turkey, and Libya in the Mediterranean, and in Mozambique, Tongaland, Kwazulu-Natal, the Malagasy Republic, islands off southern Arabia, and Western Australia around the Indian Ocean. In the Pacific Ocean, nesting occurs in Japan, eastern Australia, Fiji, the Solomon Islands, and western Mexico (Pritchard, 1979).
Geographic Variation
Two poorly marked subspecies have been described. Caretta caretta caretta (Linnaeus, 1758), the Atlantic loggerhead, ranges from Newfoundland and the British Isles south to Argentina, the Canary Islands, and the western coast of tropical Africa; occasionally it enters the Mediterranean Sea. This turtle commonly has seven or eight neural bones in the carapace and averages 12 marginal scutes on each side. Caretta c. gigas Deraniyagala, 1933, the Pacific loggerhead, occurs from Alaska, Russia, India, and Kenya south through the Pacific and Indian oceans to Chile, Australia, and South Africa; it has also been recorded from the eastern Atlantic. This form has 7-12 neural bones in the carapace, the last 1-5 commonly interrupted by costal bones, and 13 marginal scutes on each side.
The validity of these subspecies has been questioned (Dodd, 1990; Márquez, 1990). Pritchard (1979) noted much overlap in number of both neural bones and marginal scutes between several populations around the world, and suggested abandoning the trinomial distinction, and Stoneburner (1980) found little variation in body depth between nesting populations of Atlantic loggerheads. Also, recent comparison of mitochondrial DNA restriction sites by Bowen et al. (1991) has revealed low divergence (0.007-0.008) between the Atlantic and Pacific populations of Caretta, indicating only recent separation of the two. It is probably best to consider the two named races as invalid.
Habitat
The loggerhead wanders widely throughout the marine waters of its range; it has been found as far as 240 km out in the open sea. It enters bays, lagoons, salt marshes, creeks, and the mouths of large rivers. The loggerhead shares its nesting beaches with the other species of sea turtles.
Natural History
Straight-line carapace lengths of mature males throughout the world are 72.2-104.1 cm (Dodd, 1988). Mature females from several nesting beaches have straight-line carapace lengths of at least 65.1-87.0 cm and average 79.2-96.4 cm (Dodd, 1988; Van Buskirk and Crowder, 1994). Since these measurements were taken from obviously mature turtles, maturity probably is attained at a shorter carapace length, perhaps 60-70 cm (Hughes, 1974). Wild North American Caretta caretta seem to reach mature size in 10-30 years (Mendonca, 1981; Frazer, 1983; Frazer and Ehrhart, 1985; Zug et al., 1983, 1986), and captives have been estimated to mature in 16-17 years (Frazer and Schwartz, 1984). Unfortunately, the physical changes during the gonadal cycles have not been adequately described for either sex. In Australia, during January-March the male's seminiferous tubules are involuted with only spermatogonia, or some primary spermatocytes and abundant secondary spermatocytes and early spermatids, and tubules have some spermatozoa in the lumen (Wibbels et al., 1990). Transforming spermatids and some spermatozoa are present in July, and from late July-October spermatids and spermatozoa are abundant, with maximal spermiogenesis in September-November. By the end of November spermatozoa are abundant, but spermatids and spermatocytes are reduced in numbers. During a nesting year, females have hundreds of vitellogenic follicles about 1.5 cm in diameter four months prior to the nesting season (Wibbels et al., 1990). By ovulation the ovarian follicles have yolked and are enlarged to approximately 3.0 cm in diameter.
Although Pritchard and Trebbau (1984) stated that "copulation takes place at the beginning of the nesting season", it may in fact occur several months before the turtles arrive at the nesting beach (Bearse, 1985; Limpus, 1985; Dodd, 1988; LeBuff, 1990). Courtship involves circling, a final approach from the rear, and neck and shoulder biting by the male (Limpus, 1985). Mating has been observed at every hour from dawn to dark but doubtless also occurs at night. Paired loggerheads may copulate for extended periods—more than three hours, according to Wood (1953)—and females may remate after each nesting (Harry and Briscoe, 1988). Mating occurs at the surface of the water. Although the female is completely submerged, the highest part of the male's carapace usually is out of the water. He grasps the anterolateral margins of her carapace with the claw of each fore flipper and the posterolateral margins with the claw of each hind flipper. He sometimes bites the nape of her neck. His tail is bent down and under hers, so that the cloacal vents touch. Female mating behavior ranges from passive acceptance to violent resistance. Females can store sperm for some time, so several males may contribute sperm to a single clutch of eggs (Harry and Briscoe, 1988; Galbreath, 1993).
Nesting is mostly carried out on temperate zone beaches (except for tropical beaches in the western Caribbean). Nests are primarily excavated on continental beaches seaward from the dune front or, secondarily, island beaches. Most nesting is in the spring or early summer, and long migrations are often made between the feeding areas and the nesting beaches. Most nests are dug at night, but occasionally during the day (Moulis, 1994), above the high tide mark. Although the females may come onto the beaches on any night during the season, most nest during periods of high tides. First a body pit is dug, and then a some-what flask-shaped nest cavity 15-25 cm deep and 20-25 cm wide.
A female may lay 1-7 clutches a season (Dodd, 1988), but average 3.49 (Van Buskirk and Crowder, 1994). The interval between successive ovipositions is 9-28 days, but more frequently 11-15 days on North American beaches (Dodd, 1988). Groups of females may nest together several times. Not all females nest each year, instead they oviposit once every 2-4 years (average 2.59; Van Buskirk and Crowder, 1994). Clutches average 112.4 eggs (Van Buskirk and Crowder, 1994), with a reported range of 23-198 (Dodd, 1988). The white eggs are spherical (34.7-55.2 mm) with leathery shells. The incubation period is 46-80 days, depending on the incubation temperature (Dodd, 1988).
Hatchlings usually emerge at night, and their emergence seems cued to lower surface temperatures. They have heart-shaped, yellowish brown to brown or grayish black carapaces (33.5-55.0 mm; average 43.8 mm; Van Buskirk and Crowder, 1994) with three longitudinal keels. The plastron also bears several longitudinal ridges. Caretta eggs incubated at 32°C or above develop into females, while those incubated at 28°C or below produce males; intermediate incubating temperatures give both males and females (Yntema and Mrosovsky, 1982).
Caretta is omnivorous. It commonly noses about coral reefs, rocky places, and old boat wrecks for food. Prey is detected either visually or by odor. Invertebrates seem the most important food groups, and its large head and massive jaws seem well-adapted for crushing hard-shelled prey. Prey consumed include: sponges, hydroids, jellyfish (including Physalia), polychaete worms, cephalopods (squid, cuttlefish), snails, whelks, conchs, pennshells, bivalves (clams, mussels, oysters, scallops), barnacles, amphipods, shrimp, crabs, brachiurans, isopods, insects, horseshoe crabs, bryozoans, sea urchins, basket stars, tunicates, fish (eggs, juveniles, adults of Brevoortia, Ceratoscopelus, Diodon, Entelurus, Hippocampus, Macrorhamphosus, Sardinops, Scomber), young turtles (Caretta, Malaclemys), algae (Ascophyllum, Sargassum, Ulothrix, Urospora), and vascular plants (Cymodocea, Thalassia, Zostera) (Carr, 1952; Van Nierop and Den Hartog, 1984; Dodd, 1988; Márquez, 1990; Burke et al., 1993a, 1993b; Ernst et al., 1994; Frick, 1997).
IUCN Red List Status (1996)
Endangered (A1abd). The loggerhead has been so consistently persecuted at the nesting grounds and so many of them destroyed that the original nesting range cannot be discerned. The rapid development of beaches and coastal islands for home sites and recreational areas probably will destroy most of the North American nesting beaches and perhaps exterminate the Atlantic subspecies. The raccoon is a most efficient nest predator, and the marked expansion of its coastal populations also threatens thefuture of C. [l][m]Glossary[/m][r]Caretta[/r]caretta. Many adults are drowned when caught in shrimp trawls. The main hope for the survival of the Atlantic loggerhead lies in the development of state and national parks and reserves, and the development of turtle-proof shrimp trawls.